Coupling for tool element

ABSTRACT

An electric grass trimming device comprising a handle including a grip and trigger switch at one end and an electric motor at the other end, the motor being arranged to drive a cutting blade mounted beneath the motor. An improved coupling arrangement between the blade and the motor shaft is described.

United States Patent Weber June 20, 1972 1 COUPLING FOR TOOL ELEMENT 3,146,007 8/1964 Boivie ..287/53 R 3 270 467 9/1966 Block... 1/358 72 l t i W B l 1 J Md 3,264,016 8/1966 Relsch.. .....287/53 R [73] Assignee: The Black and Decker Manufacturing 3,342,273 9/1967 Crane ..287/52.4 p y, TOW-S011, 3,436,875 4/1969 Cheney.... ..5 l/ 376 [22] Filed: Aug. 21, 1970 Primary Examiner-Trav1s S. McGehee PP N03 65,953 Assistant Examiner-J. C. Peters Attorney-Leonard Bloom and Joseph R. Slotnik [52] -U.S. Cl ..30/276, 51/376, 56/295 51] Im. c1 ..B26b 25/00 [57] ABSTRACT [58] Field of Search ..30/240, 264, 276, 347; An electric grass trimming device comprising a handle Includ- 287/52'04 53 15/49 56/295 51/376 ing a grip and trigger switch at one end and an electric motor 383 at the other end, the motor being arranged to drive a cutting blade mounted beneath the motor. An improved coupling ar- [56] References cued rangement between the blade and the motor shaft is UNITED STATES PATENTS described- 2,539,619 1/1951 Goodall ..30/276 3 Claims, 6 Drawing Figures ill ll fi l PATENTE'Daunzomz I Y 3 670;413

INVENTOR EDWIN J. WEBER ATTORNEY COUPLING FOR TOOL ELEMENT The present invention is directed to an insulating coupling device for motor shafts and is specifically directed to an insulative coupling which incorporates a slip means to reduce damage.

' Electric motor driven devices usually include a direct connection between the output shaft of the motor or gear spindle and the working element. This can be the cause of both damage to the device and injury to the operator or another object, since there is no means for limiting the force transmitted, if a careless or accidental movement causes the element to contact some obstruction.

This is particularly true in the case of devices having cutting blades for purposes such astrimming or mowing grass, since rocks, fences, and other hard objects are frequently encountered accidentally. Also, in the case of such devices, the blade may cut the electrical power cord, producing the possibility of shock if the operator is in electrical contact with the blade. Accordingly, it is desirable to have a coupling device which insulates the various parts against mechanical damage and against electrical contact.

It is the purpose of this invention to provide an improved coupling means which overcomes these disadvantages.

Accordingly, it is an object of this invention to provide an improved attachment means for the output element of electric tools.

Another object of this invention is the provision of an inexpensive blade mounting device for electric grass trimmers which incorporates clutch means to reduce breakage and insulating means which provides coupling without electrical conductivity.

These and other objects of the present invention will become more apparent as the description and illustration thereof proceed.

In the drawing,

FIG. 1 is a perspective view of a device embodying the present invention;

FIG. 2 is a plan view of a part of the device of FIG. 1;

FIG. 3 is an exploded view corresponding to FIG 2;

FIG. 4 is a perspective view of an integral blade and blade mounting means in accord with this invention;

FIG. 5 is a cross-sectional view taken on the lines 55 of FIG. 4; and

FIG. 6 is an exploded perspective view of an alternative construction in accord with the present invention.

Briefly, in accord with one embodiment of this invention, a grass trimmer is provided which includes a handle, an electric motor at one end of the handle, and a blade mounted on the shaft of the motor for cutting grass by means of an improved coupling arrangement. This coupling includes an insulating member secured to the endof the shaft and a blade mounting means which engages the insulating member and secures the blade thereto. Preferably, the insulating member comprises a cylindrical body having a groove in its surface and the blade mounting means includes a plurality of spring clips which engage in the groove. In accord with further features of this invention, the insulator may be a molded part which also provides a cooling fan, and the blade and blade mounting means may be formed from a single metal piece. This coupling may also be used for attaching other output devices to an electric motor. Further features and possible modifications of this em bodiment will be apparent from the following description.

In FIG. 1, the device illustrated comprises a small trimmer for use, for example, in trimming small grassy strips adjacent bushes, fences, flower beds, etc., which may be difficult to cut with a lawnmower. The trimmer comprises a housing 10 which covers an electric motor, not shown. A guard member 11 is mounted on the housing and encloses a blade 12 which is disposed at the end of a shaft extending from the trimmer. The trimmer also includes an extended handle 9 and grip 8 which is adapted to be grasped by the operator. The trimmer may be connected to a source of power via an extension card, not shown, and the operator controls the energization of the motor by means of a trigger switch 7.

FIGS. 2 and 3 illustrate a preferred embodiment of the coupling arrangement of this invention. As shown therein, the blade 12 is supported by means of a plurality of spring clips 13 which are engaged with an insulating member 14. The insulating member of hub 14 is supported at the end of a shaft 15, for example, by being press-fitted over a knurled portion adjacent the end of the shaft. A bearing 16 supports the shafi 15 for rotational movement and a washer 17 may be provided between the bearing and the hub.

In accord with a preferred embodiment of this invention, the insulating hub 14 comprises a molded member, a portion 18 of which is shaped to provide fan blades which draw cooling air through the motor. Extending downwardly from the fan blades is a generally cylindrical portion which includes a recess in the fonn of an annular groove 19 in its surface. Below the annular groove, there is a cylindrical portion 20 of increased diameter. The portion 20 is rounded so as to easily accommodate the spring clips 13 which mount the blade.

As shown in FIGS. 4 and 5, a preferred embodiment of this invention utilizes a combined construction for the blade holding means and blade. Thus, the blade 12 and spring clips 13 are formed from a single piece of sheet metal, a stiffening rib 21 also being provided in the blade during the forming operation. Thus, the blade is mounted by simply pressing the spring clips 13 over the cylindrical portion 20 of the insulating hub until the inwardly curved portion of the spring clips engage the annular groove 19.

FIG. 6 illustrates an alternative construction wherein the spring clips 13 are formed separately from the blade 12. In this instance, the spring clips are joined by a central web of metal 22 which engages the blade 12 and holds it securely against the bottom of the hub.

It will be apparent to those skilled in the art that many changes and modifications can be made without departing from the spirit of this invention. For example, a blade design incorporating a single radial extending arm or designs incorporating three or four radially extending arms could be used if desired. It is also noted that other forms of cooperating detent means could be used as the blade mounting means; such as the use of a plurality of narrow circumferentially spaced recesses, each of which is engaged by a single spring clip. Also, an internal opening within the center of the insulating hub into which a male detent is inserted and engages the hub by means of a radially outward spring force could be provided if desired. In any of these cases, the features of insulating the blade from other metallic parts of the unit and that of providing a slip clutch to reduce blade breakage are retained. Of course, as previously noted, the coupling of this invention may also be applied to the attachment of other output devices, as long as the torque requirements are not excessive. Accordingly, it is intended that the appended claims cover all such changes and modifications as may come within the spirit and scope of this invention.

I claim:

1. In a portable, hand-held grass trimming device including an electric motor, a housing for said motor and a handle extending from said housing; said motor having an output shaft extending therefrom, and an elongated cutting blade mounted at the end of said output shaft for cutting grass upon rotation of said shaft, the improvement comprising an insulating coupling member mounted on the end of said shaft, said member having an annular groove in the surface thereof; and means for retaining said blade tightly against the end of said member, said retaining means and said blade being insulated from said shaft by said member; said retaining means comprising spring means coupled to said blade and engaged in said groove, said spring means providing a slip clutch drive for said blade.

2. The combination claimed in claim 1 wherein said spring means comprises an integral extension of said blade.

3. The combination claimed in claim 1 wherein said spring means comprises an independent, cup-shaped member for receiving said blade and including spring elements for engaging in said annular groove. 

1. In a portable, hand-held grass trimming device including an electric motor, a housing for said motor and a handle extending from said housing; said motor having an output shaft extending therefrom, and an elongated cutting blade mounted at the end of said output shaft for cutting grass upon rotation of said shaft, the improvement comprising an insulating coupling member mounted on the end of said shaft, said member having an annular groove in the surface thereof; and means for retaining said blade tightly against the end of said member, said retaining means and said blade being insulated from said shaft by said member; said retaining means comprising spring means coupled to said blade and engaged in said groove, said spring means providing a slip clutch drive for said blade.
 2. The combination claimed in claim 1 wherein said spring means comprises an integral extension of said blade.
 3. The combination claimed in claim 1 wherein said spring means comprises an independent, cup-shaped member for receiving said blade and including spring elements for engaging in said annular groove. 